Design Of A Low-power And High Linearity Cmos Down-conversion Mixer

According to the current development of the CMOS RFIC and the wireless communication technology, combined with monolithic integrated requirements of the three parts (RF, IF and baseband circuit), CMOS RF down-conversion mixer for 802.11g communication system is designed.Firstly, the necessity of designing the research of CMOS RF mixer for 802.11g communication system is discussed by analyzing the actuality of the WLAN development and the unique advantage of the 802.11g technology. The mixing principle and technical indicators is analyzed deeply. Summarized some key frequency parameters that will be used in design.Secondly, based on RFIC design flow and comparison of production technology, selected a full CMOS process technology of high integration, low power and easy to produce, and analyzed the RF equivalent model of the device in detail. According to 0.25 um RF spice file of TSMC, Devices model including NMOSFET, Inductors on chip, Capacitors on chip, Resistors on chip is studied deeply, selected MIM capacitors and spiral inductors with the best overall performance.Thirdly, optimization of CMOS down-conversion mixer circuit is designed. Based on the traditional Gilbert mixer circuit, Transconductance-level uses CMOS gm cell structure, the three differential pair to replace the original circuit on a differential pair to extend the linear operating range, concerted the input RF voltage signal into a current signal, as bias current of the Switch-level. Transconductance-level increase the RF, IF, the LO three-port isolation between them, thus enhancing the transconductance of the mixer, and ultimately improve the overall circuit gain and linearity. Switch-level using Gilbert double-balanced structure, the RF current signal is converted to IF current signal, and can improve the linearity and isolation also; LC tank is taken into the structure to achieve low-voltage and high-performance. Load-level can convert IF current signal into the IF voltage signal, Load-level select active load structure of resistor in parallel with PMOS, it can improve the output voltage, thereby increasing the gain. Three parts of the bias current is provided by the current mirror source circuit.Lastly, combined with the circuit principle, simulated the mixer circuit with ADS2008 soft ware. Tested the parameters of mixer circuit show that the design have accomplished the requirements fully. proved the design is right.